Compressor/Water Pump Part IV
Pilot Valve Stem, Test & Installation
Nelson Riedel Nelson@NelsonsLocomotive.com
Initial: 1/13/04 Last
|Valve Test: I decided to test the steam valves at this
point before going any further with the fabrication. The pilot
valve stem assembly in the upper photo was made from 3/16"
brass and a 2-56 threaded rod (screw with head cut off). The lower photo
shows the valve assembly with the end of one 3/16" brass rod
sticking out below the head. Compressed air was
then connected via the hose and the valve operation tested by
pushing and pulling the 3/16" rod. Well, it didn't
work, and there seem to be air leaks everywhere. I
took it apart and double checked everything ---- nothing seemed to
be amiss. As a last resort I verified that the air was
connected to the input port. Damn! Should have checked that
Once air was supplied to the input port the valve worked as
expected (maybe hoped is more correct). The shuttle
operated with some authority with as little as about 15
|Valve Stem: The photo shows the final valve
stem. The brass pieces are 3/16" rod. The left
piece and left half the middle piece are threaded 2-56, the screw
on the left and the stainless threaded rod over the valve
are also 2-56. The stainless steel piece on the
right is 1/8" OD threaded 5-40 on the ends. The screw
in the right end is 4-40 stainless steel. The disk screws to
the top of the steam piston.
|This photo shows the valve stem position when the the piston is
against the stops at the top of its travel. The middle brass piece
was cut to the exact length required so that the valve is positioned
in the upper extreme position. The screw on the
left is cut so that it's all the way in and against the end of the 2-56
threaded rod. The valve is loose in the gap
between the two brass pieces.
|This shows the valve stem position when the piston is against the
stops at the bottom of its travel. The brass piece
inside the piston rod was adjusted so that the valve was in the
lower extreme position. The screw in the right (lower) brass piece was then
cut so that it was all the way in the brass piece and against the
end of the 1/8" rod. After the pump was tested and the
valve stem adjustment was shown to be correct, #620 (high
temperature) Loctite was applied to all the threads except the
joint between the brass piece inside the piston rod and the
Update 5/16/04: The pump failed several
times due to the pilot valve rod and the connection between the shuttle
valve pistons working loose. I finally bit the bullet and took apart
each joint and applied high temperature Loctite (620) which seems to have
fixed the problem. End update.
The valve stem is removed by inserting a hex wrench up
through the the lower end of the piston rod and a flat blade screwdriver down
through the top of the pilot valve cylinder into the screw head above the
valve. The joint inside the piston rod can then be unscrewed and the
stem with the valve can then be pulled up and out the top of the pilot valve
The pilot valve can be removed using the following
Remove the cap and bushing at the top of the pilot valve
Remove the lower pump cylinder head.
Remove the set screw in the bottom of the piston rod.
Push the piston to the upper extreme position.
Insert a hex wrench or small rod in the piston rod and
push the valve stem to the upper position.
With both the piston and valve stem in the upper
position, much of the valve stem and the valve sticks out
above the top of the pilot cylinder. The valve can then be pulled away
from the stem
Once the valve has been removed, the upper head can be
removed if necessary.
This procedure can be reversed to reinstall the
First Steam Test (using compressed air): The steam side of the system was then assembled and
tested on compressed air. It didn't work very well --- it was very erratic.
I then put a little water in the air line and it straightened right and
worked pretty well. The water serves to lubricate everything and
help the valves seal. I was curious how the system would work
with a little lubricant. Petroleum based lubricants are not compatible
with the EPDM O-Rings but brake fluid is so I tried a half dozen drops in
the air line. Wow! The thing took of and was really smooth, worked
down to a few pounds of air pressure. I let it run for a half hour or
so and it worked great, never hung up once. I then installed the water pump cylinder
and piston and it continued to operate great.
After this successful test I took a break. Later
I tried it again and it was erratic again. The valve seemed to be
working but the steam piston seemed to be hanging up. Pulled the
piston and found the O-Ring had turned soft and failed. Then I
remembered, McMaster Carr doesn't carry the high temperature EPDM
version of the #121 O-Ring so I got a bag of 100 of #121 Buna-N O-Rings for
a couple dollars. This test confirmed the O-Ring literature; Buna-N is
not compatible with brake fluid.
The plan was to order the correct O-Ring from Marco Rubber
once I was sure of the correct size. Marco seems to have a minimum
price of $10 per item. In this case one of the O-Rings is $10 and one
can also buy 100 of the #121 O-Rings for $10.00. I also need some of the #008 size
used for the valve stem seals and can get 100 of these for $10 and 500 for
$10.40. (I had a bunch of the #008 in the 200
degree max temperature EPDM that I'd used in brake systems. McMaster
Carr doesn't carry the #008 size in the higher temperature EPDM
either. ) Guess I'm going to end up with a few hundred spare O-Rings.
Update 2/23/2006: I changed the O-Rings to Viton for
everything except the water piston which was changed to Buna-N.
I obtained the Viton and Buna-N O-Rings from from McMaster-Carr.
The brake fluid lubricant worked great so that I'm considering
building a lubricator. Also, a few drops of that stuff might loosen
up those steam brake pistons a bit --- makes sense, brake fluid for brake
cylinders. However, the polyglycol ether based braked fluids
(DOT3, DOT4 & DOT5.1) are some of the most effective paint
removers known to man. Don't want that stuff around my
locomotive since I hope to paint it someday. These brake fluids are soluble in water
so the lubrication might also wash off pretty easily. An alternative
is the silicone brake fluid (DOT5). The silicone fluid is harmless to
paint and isn't soluble in water. So, maybe a lubricator that
uses the silicone fluid. Some further tests are in
order. Update:2/23/2006: After changing the steam side O-Rings
to Viton I was able to use standard steam oil for lubrication.
See added lubricator at the end. End Update.
|Lower Head: The lower head on the water pump was the
last operational part to be finished. A piece of 3/4" Brass rod was
turned to fit inside the pump cylinder (5/8" OD) and a recess
bored to accommodate the the nut on that holds the pump piston
to the piston rod. This piece was then silver soldered to the
head. The photo shows the head with with the
short (~.030") shoulder that fits into the pump
|This photo shows the under side of the head. The pinkish
color is strain from the flux used when the pieces were silver soldered together.
|It Works! Everything was assembled for a test of the
complete pump. The unit seemed very stiff so a few drops of
silicone brake fluid was added to the air line ---- it seemed to
work even better than with the glycol based fluid. Next the sink
was partially filled with water, a hose connected
to the water input with the other end in the sink. The air was
connected and the pump started up. The output sputtered for a
couple seconds and then shot a stream about 20 foot across the
room. (Fortunately I was using the workshop sink; she'd have
killed me if she caught me doing something like this in her kitchen
sink.) About as much water came out around the pump
heads as the output pipe. The heads were attached with only
|Mount: The last major task was to make the
mount. A 3/8" wide slot was milled in the back of the
steam cylinder and the 1/4" X 3/8" mounting bar was
soldered in the slot. The holes in the ends of the
mount are for 6-32 screws.
Gaskets were then made for the cylinder heads, shuttle valve
heads and between the upper head and the steam valve assembly.
The shuttle valve head screws were replaced with studs and
nuts. All the head screws were then installed
and the pump tested again. The gaskets and screws seemed to
fix the leaks.
Further tests are required under steam pressure pumping water
against 100 psi boiler pressure. However, don't think there
will be a problem.
|This shows the finished pump. The pump will have to be
partially disassembled later to install the correct EPDM
O-Rings on the steam cylinder piston and for the valve stem
seals. The socket head cap screws connecting the tie piece to
the two cylinders will be replaced with hex head screws at that
time. The socket head screws are easy to install and
remove using a
ball end hex wrench which was convenient when multiple assemblies and
disassemblies were required during the fabrication. The hex
head screws are more time consuming to install since an open end
wrench is used.
This pump has been one of the most rewarding parts of the shay
project. It would be a good project for one to do prior to
attempting a locomotive since a number of different skills are
required yet the project is fairly small and the finished pump can
function as a self contained unit.
Update 1/30/2004: Yesterday (1/29/2004) I used
the pump on compressed air to fill the boiler and then wheeled the
locomotive outside in the 15 degree (F) weather to do a steaming test.
The pump worked on steam just as it did on compressed air. With the
cold temperature it was easy to spot two steam leaks. One leak
was from the slot I milled for the mounting bar. This milled
slot cut through the steam passage from the shuttle valve to the bottom of
the steam cylinder. The mounting bar was silver soldered in place
which sealed the steam passage except for a pin hole. The other leak
was from the joint between the valve case and the upper head. The pump
was disassembled later and the pin hole was soldered shut. A
high spot was found that kept the valve case from seating on the head.
After the high spot was filed off the valve case/head joint
There was no problem starting the pump. The pump was
started and then stopped and allowed to cool a half dozen times. There
was clearly condensate in the valves and cylinder that didn't seem to interfere
with starting even at very low pressure. After the two leaks were
fixed the pump was submerged in water to allow the steam cylinder and valves to
fill with water. The pump started on less than 50 pounds pressure
every time, even under water . This thing is reliable!
Update 6/6/04: The
pump started to run really slow. A few drops of silicone brake fluid
in the steam line speeded it up for a few minutes but then it slowed down
again. A lubricator seemed like a real pain. The pump was
disassembled and the steam piston was found to be hard to push. A little
water made it easier to push but still pretty tight. The depth
of the gland was according to specifications --- but that was for a tight
seal. For this application a slight leak is tolerable so the gland
depth was increased to 0.100" --- a loose seal for the 0.103"
O-Ring cross section. The pump has run flawlessly after this fix and
the application of Loctite to the valve joints.
|Update 2/23/2006: As mentioned
previously, the EPDM O-Rings became sticky after a couple years of use
so I changed to Viton O-Rings on the steam piston, steam valves and
rod seals. I also added the displacement lubricator shown
on the right. The lubricator was obtained from American Model
Engineering Supply, model DLU4. The unit seems to run a bit
freer than before.